diff --git a/best-time-to-buy-and-sell-stock/yhkee0404.go b/best-time-to-buy-and-sell-stock/yhkee0404.go
new file mode 100644
index 000000000..4379b18c0
--- /dev/null
+++ b/best-time-to-buy-and-sell-stock/yhkee0404.go
@@ -0,0 +1,9 @@
+func maxProfit(prices []int) int {
+    ans := 0
+    bought := prices[0]
+    for i := 1; i != len(prices); i++ {
+        ans = max(ans, prices[i] - bought)
+        bought = min(bought, prices[i])
+    }
+    return ans
+}
diff --git a/encode-and-decode-strings/yhkee0404.java b/encode-and-decode-strings/yhkee0404.java
new file mode 100644
index 000000000..367f757e0
--- /dev/null
+++ b/encode-and-decode-strings/yhkee0404.java
@@ -0,0 +1,44 @@
+public class Solution {
+    /*
+     * @param strs: a list of strings
+     * @return: encodes a list of strings to a single string.
+     */
+    public String encode(List<String> strs) {
+        // write your code here
+        return strs.parallelStream()
+                .map(s ->
+                    s.chars()
+                            .parallel()
+                            .mapToObj(c -> new StringBuilder(String.format("%02x", c)))
+                            .collect(
+                                StringBuilder::new,
+                                StringBuilder::append,
+                                (a, b) -> a.append(b)
+                            )
+                ).collect(
+                    StringBuilder::new,
+                    (a, b) -> a.append(b)
+                            .append(' '),
+                    (a, b) -> a.append(b)
+                ).toString();
+    }
+
+    /*
+     * @param str: A string
+     * @return: decodes a single string to a list of strings
+     */
+    public List<String> decode(String str) {
+        // write your code here
+        final List<String> ans = new ArrayList<>();
+        final StringTokenizer st = new StringTokenizer(str);
+        while (st.hasMoreTokens()) {
+            final String s = st.nextToken();
+            final StringBuilder sb = new StringBuilder();
+            for (int i = 0; i < s.length(); i += 2) {
+                sb.append((char) Integer.parseInt(s.substring(i, i + 2), 16));
+            }
+            ans.add(sb.toString());
+        }
+        return ans;
+    }
+}
diff --git a/group-anagrams/yhkee0404.rs b/group-anagrams/yhkee0404.rs
new file mode 100644
index 000000000..6ba9c3cb9
--- /dev/null
+++ b/group-anagrams/yhkee0404.rs
@@ -0,0 +1,30 @@
+use itertools::Itertools;
+
+impl Solution {
+    pub fn group_anagrams(strs: Vec<String>) -> Vec<Vec<String>> {
+        let sorted_strings: Vec<String> = strs
+                .iter()
+                .map(|s| {
+                    s.chars()
+                            .sorted()
+                            .collect()
+                }).collect();
+        let inverted_sorted_strings: Vec<usize> = (0..sorted_strings.len())
+                .sorted_by_key(|&i| &sorted_strings[i])
+                .collect();
+        let mut ans: Vec<Vec<String>> = vec![];
+        let mut i = 0;
+        let mut j;
+        while i != sorted_strings.len() {
+            let mut u: Vec<String> = vec![];
+            j = i;
+            while j == i || j != inverted_sorted_strings.len() && sorted_strings[inverted_sorted_strings[i]] == sorted_strings[inverted_sorted_strings[j]] {
+                u.push(strs[inverted_sorted_strings[j]].clone());
+                j += 1;
+            }
+            ans.push(u);
+            i = j
+        }
+        ans
+    }
+}
diff --git a/implement-trie-prefix-tree/yhkee0404.dart b/implement-trie-prefix-tree/yhkee0404.dart
new file mode 100644
index 000000000..48dbc276d
--- /dev/null
+++ b/implement-trie-prefix-tree/yhkee0404.dart
@@ -0,0 +1,40 @@
+class Trie {
+
+  final int n;
+  final children = <int, Trie>{};
+  bool ended = false;
+
+  Trie([this.n = 0]);
+  
+  void insert(String word) {
+    Trie u = this;
+    for (int rune in word.runes) {
+        u = u.children
+                .putIfAbsent(rune, () => Trie(rune));
+    }
+    u.ended = true;
+  }
+  
+  bool search(String word) => _search(word)?.ended ?? false;
+  
+  bool startsWith(String prefix) => _search(prefix) != null;
+
+  Trie? _search(String word) {
+    Trie? u = this;
+    for (int rune in word.runes) {
+        u = u!.children[rune];
+        if (u == null) {
+            return null;
+        }
+    }
+    return u;
+  }
+}
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * Trie obj = Trie();
+ * obj.insert(word);
+ * bool param2 = obj.search(word);
+ * bool param3 = obj.startsWith(prefix);
+ */
diff --git a/word-break/yhkee0404.scala b/word-break/yhkee0404.scala
new file mode 100644
index 000000000..a009183cb
--- /dev/null
+++ b/word-break/yhkee0404.scala
@@ -0,0 +1,16 @@
+object Solution {
+    def wordBreak(s: String, wordDict: List[String]): Boolean = {
+        val dp = Array.fill(s.length + 1)(false) // S(s, wordDict, word) = O(s.length)
+        dp(0) = true
+        (0 to s.length - 1).exists { i =>
+            if (! dp(i)) false
+            else wordDict.exists { word =>
+                        val j = i + word.length
+                        if (j <= s.length && ! dp(j) && s.substring(i, j) == word) {
+                            dp(j) = true // T(s, wordDict, word) = O(s.length * wordDict.length * word.length)
+                        }
+                        dp(s.length)
+                    }
+        }
+    }
+}